Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$7.38	6.148%	$7.8337	$7.83	$7.85	$7.80
Purchase #2	$138.38	5.236%	$145.6256	$145.63	$145.65	$145.60
Purchase #3	$98.54	10.190%	$108.5812	$108.58	$108.60	$108.60
Purchase #4	$31.50	3.769%	$32.6872	$32.69	$32.70	$32.70
Purchase #5	$242.92	9.275%	$265.4508	$265.45	$265.45	$265.50
Purchase #6	$217.68	8.661%	$236.5333	$236.53	$236.55	$236.50
Purchase #7	$189.96	13.449%	$215.5077	$215.51	$215.50	$215.50
7 purchase totals =	$926.36		$1,012.2195	$1,012.22	$1,012.30	$1,012.20